This invention relates to a casing of a hydraulic machine, more particularly a casing of a hydraulic machine wherein the hydraulic characteristics of the machine are improved by decreasing the size of stay vane flow passages defined between a plurality of stay vanes fixed between a pair of annular plates.
The stay ring of the casing of a modern hydraulic machine, typically a pump and a water turbine, comprises a plurality of stay vanes fixed between vertically spaced annular plates for defining a plurality of stay vane flow passages between the stay vanes.
When the hydraulic machine is operated as a water turbine, water flows from the spiral chamber of a spiral case to a runner chamber successively through the stay vane flow passages and the guide vane flow passages to rotate the runner and then discharged into a draft tube.
With the stay ring having the construction described above, however, as the cross-sectional area varies rapidly at the boundary between the spiral chamber of the spiral case and the stay vane flow passages, the velocity of the water varies when it passes through the boundary thus increasing the loss in the hydraulic head due to shock of the water flow (shock head loss). Furthermore, in the prior art casing, for the purpose of decreasing the loss in the hydraulic head caused by friction (friction head loss) which is proportional to the square of the velocity of the water flowing through the spiral case it has been the practice to design the cross-sectional area of the flow passage of the spiral case to be as large as possible. This not only increases the cost of manufacturing the spiral case but also increases the variation in the cross-sectional area at the boundary thereby increasing the shock head loss.